This invention relates to an audio-visual system and, more particularly, to an improved sound motion picture system employing a multipurpose, photographic film handling cassette. Multipurpose motion picture cassettes from which the film need not be removed during exposure, processing and projection operations are described in prior U.S. Pat. Nos. 3,615,127 of Edwin H. Land, issued Oct. 26, 1961; 3,600,071, issued to Rogers B. Downey on Aug. 17, 1971; and 3,895,862 issued to Joseph A. Stella, et al., on July 22, 1975. Each of the systems described in the aforementioned patents employs a cassette from which the film need not be removed during exposure, processing and projection operations. In these systems, the cassette is operated in the camera for exposure of the film strip and then subsequently, the cassette is loaded into a projector apparatus which first subjects the cassette to a sequence of operations which process the film strip to a viewable condition and then subsequently projects the developed recorded images.
Advantageously, audio operations may also be included in the described cassette system. Exemplary of such an audio-visual system is that described in prior U.S. Pat. No. 3,604,790 of Edwin H. Land, et al. issued Sept. 14, 1971 and U.S. Pat. No. 3,856,387 of William R. Wray, et al. issued Dec. 24, 1974. These latter patents describe a film handling cassette in which the film is permanently retained during sound recording and playback as well as exposure, processing and projection operations. In the latter arrangement, a magnetic sound recording track is included along one or both of the longitudinal borders of the film strip. While these systems provide generally acceptable audio reproduction, the inherent restriction of the narrow path width of the audio tracks, which cannot be allowed to interfere with the image retaining portion of the film strip lying therebetween, limits the level of sound quality which may be achieved, or conversely, substantially increases the sophistication and cost of the sound apparatus necessary for high fidelity stereo reproduction.
A preferred solution to this problem is shown in copending U.S. patent application Ser. No. 869,131 assigned to the assignee of the present application, which application describes an arrangement wherein a photographic film strip and an audio information bearing tape are interwound on a common supply spool and simultaneously unwound from the spool and advanced synchronously along separate paths such that different operational functions may be provided on the film and the tape as they progress along their different paths. In the preferred embodiment, both the film strip and the sound tape are substantially retained within a multipurpose film cassette of the type described above while they are advanced along different, diverging paths from the supply spool to a separate takeup spool where they are again interwound with one another.
In a preferred embodiment of such a cassette employing a film strip and a magnetic tape interwound on common supply and takeup spools, the audio tape is passed through an opening in a cassette wall to the exterior of the cassette to provide access to the tape by the audio drive system and the sound recording and playback transducer. The tape is then guided by suitable means through another opening back into the cassette, and from there it passes to the other of the film spools. Further, with such an arrangement, the length of the magnetic tape extending along its path from one spool to the other is such that it contains a slack loop or portion thereof which permits formation of isolating loops in the tape both before and after contact with the audio transducer and tape drive in order to isolate the portion of the tape being advanced across the transducer at a constant speed from the intermittent advancement of the film strip. Such isolation is necessary in order to obtain the high quality high fidelity stereo sound which is desired. While the described free loop of magnetic recording tape is necessary for operation of the cassette in the recording and playback modes of operation, the loop serves no function during the processing mode of operation of the cassette (i.e., its first rewind) and during subsequent rewinds. Further, it is undesirable to have the free loop extending from the cassette when the cassette is not in operational engagement with either a camera or projector as the possibility of abuse and possible damage to the tape is high if the cassette is not handled extremely carefully.